Are spells with saving throws balanced?

@danglading @JeremyECrawfordAre spells with saving throws balanced such that rolling crit damage on a 1 would break things? spells tend to deliver big bursts of damage – would be deadlier than most weapon crits.

— Mike Mearls (@mikemearls) November 20, 2015

@danglading @JeremyECrawford that said, if you're OK with that added layer of peril go for it. It's a nifty idea for the right campaign

— Mike Mearls (@mikemearls) November 20, 2015